As intriguing as topological defects might be, crystals made out of them appear to be even more exotic, like the soliton lattice that forms in doped polyacetylene [1]}, for instance. Examples of topological defect lattices abound in Condensed Matter Physics where one might find lattices of parallel screw dislocations in solids [2]}, vortex lattices in rotating superfluids [3]} and in Bose-Einstein condensates [4]}, as well as the much studied magnetic flux lattices in type II superconductors [5]}. Liquid crystals contribute with lattices of disclinations in nematics [6]}, and with lattices of screw dislocations in cholesterics (known as twist grain boundaries) [7]}. Nevertheless, the most fascinating topological defect lattices are found in the realm of chiral liquid crystals [8]} where skyrmions [9]}, hopfions (3D skyrmions) [10]}, merons (half-skyrmions) [11]} and even knots [12]} may form regular arrays. Off this planet one might have magnetic flux tube lattices in neutron stars [13]} and crystals of cosmic strings or of cosmic domain walls, which have been considered as possible candidates for solid dark matter models [14]}, [15]}. All this zoo of topological defects shares a common origin: phase transitions involving break of symmetry. Not surprisingly thus, the Kibble-Zurek mechanism [16]}, [17]} of defect formation applies both to cosmic strings and disclinations in nematic liquid crystals [18]}. A common feature of most of the aforementioned topological defect crystals is a logarithmic interaction of line defects in the lattice, for large enough separation between them, so the defect internal structure may be neglected. This leads to the problem of performing infinite log sums, much tackled in the 1990's.
